Energy storage technologies (such as pumped hydro, compressed air energy storage, various types of batteries, flywheels, electrochemical capacitors, etc.) provide for multiple applications that include energy management, backup power, load levelling, frequency regulation, voltage support, and grid stabilisation. Importantly, not every type of storage is suitable for every type of application, motivating the need for a portfolio strategy for energy storage technology. There are four challenges related to the widespread deployment of energy storage. The challenges are cost competitive energy storage technologies (including manufacturing and grid integration), validated reliability and safety, equitable regulatory environment, and industry acceptance. This book sets out potential options to improve energy storage. It also presents a number of specific actions that could help maintain both scientific advancements and a pipeline of project deployments.